1. Field of the Invention
The present invention relates to a method for fabricating a contact. More particularly, the present invention relates to a fabrication method for a cobalt-salicide contact.
2. Description of Related Art
Contact is one structure of an interconnect. A contact is typically formed by forming an oxide layer on a silicon substrate, followed by forming an opening In the oxide layer. The opening is then filled with a metal layer. Chemical mechanical polishing (CMP) is further used to remove the metal layer outside the contact.
The current fabrication technique for a contact includes forming a salicide material covering the substrate at the bottom of the contact. Cobalt-salicide, which has a crystalline structure similar to the silicon substrate, is often used in fabricating a contact. However as the ULSI process advances to 0.18 microns and below, the aspect ratio of the contact becomes even higher. The contact barrier layer formed by physical vapor deposition can not cover the bottom of the contact. The unreacted cobalt layer at the bottom of the contact is affected by oxygen gas and the nitrogen gas used in the process, leading to the problem of an undesirable cobalt consumption and an eventual lowering the reliability of the contact.
Accordingly, the present invention provides a technique for fabricating a cobalt-salicide contact, wherein the reliability of the contact is improved.
The present invention also provides a method for fabricating a cobalt-salicide contact, wherein an undesirable consumption of cobalt is prevented to facilitate the fabrication of cobalt-salicide.
The present invention further provides a cobalt-salicide contact fabrication technique, wherein charge loss due to mobile ions on the contact sidewall is prevented.
In accordance to the present invention, a cobalt-salicide contact fabrication technique is provided, wherein a contact opening is formed on the substrate. An aspect ratio of the contact opening can be, for example, greater than 10. A silicon nitride spacer is further formed on the sidewall of the contact opening. A cobalt layer is then deposited, followed by sequentially depositing an ionized metal plasma (IMP) titanium layer and a chemical vapor deposited (CVD) titanium nitride layer as a capping layer. A first rapid thermal process (RTP) is performed to induce a reaction between the cobalt layer and the silicon substrate to form cobalt-salicide. A wet etching is further performed to remove the titanium/titanium nitride layer and the unreacted cobalt layer. A second rapid thermal process is performed, followed by filling the contact opening with a conductive layer.
The present invention also provides a method for fabricating a cobalt-salicide contact. A deep submicron contact opening Is first formed. A silicon nitride spacer is formed on the sidewall of the contact opening. A cobalt layer is deposited, followed by sequentially forming an IMP Ti layer and a CVD TiN layer. A rapid thermal process is performed. A conductive layer, for example, tungsten is then used to fill the contact opening. Chemical mechanical polishing is further used to remove the conductive layer, the titanium/titanium nitride layer and the cobalt layer outside the contact opening.
According to the present invention, an IMP process is used to form a titanium layer with a good step coverage. A titanium nitride layer formed by chemical vapor deposition is also provided to form a cobalt-salicide contact with an aspect ratio greater than 10. The reliability of a deep sub-micron contact is thus enhanced.
In accordance to the present invention, due to the oxygen gettering ability of the Ti/TiN layer, the cobalt layer is prevented form being oxidized and consumed due to the presence of oxygen. The present invention provides a titanium/titanium nitride layer as a capping layer to prevent the cobalt layer from contacting with the nitrogen gas and from being consumed during the RTP process.
Further, the present Invention provides a titanium layer to separate the cobalt layer from the chemical vapor deposited titanium nitride layer. The cobalt layer is thus prevented from being contaminated by the impurities in the CVD TiN layer.
Additionally, the present invention also provides forming a silicon nitride spacer on the sidewall of the contact after the formation of the contact opening. As the device dimension is further being scaled down, charge loss due to mobile ions on the sidewall of the contact is prevented.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.